This invention relates to glycerol esters (glycerides) of eicosapentaenoic acid which is hereafter abbreviated as "EPA", processes for preparing the same and oil and fat products containing the same.
As one of fatty acids in fish oil, EPA abundantly exists in the natural world. Highly unsaturated fatty acids such as EPA have been noted from the standpoint of the science of nutrition. In particular, since J. Dyerberg has reported in "The Lancet." July 15, 117 (1978) that the unsaturated fatty acids of the kind are effective for prevention of geriatric diseases, the study thereof has been made actively. Further, since the acids are known to play an important role in maintenance of life as starting materials of prostaglandins, application thereof to medicines and supplementary foods for promoting nutrition has come to be expanded.
As stated above. EPA exists as a fatty acid component of fish oils and the like in the natural world, and the EPA content in various fish oils is approximately 16.5% in krill oil, 15.8% in sardine oil. 12.6% in walleye pollack liver oil, 10.2% in cuttlefish oil, 8.1% in mackerel oil, 4.9% in saury oil and 5.6% in shark liver oil. There is a low temperature crystallization process as one of the processes for separating and purifying glycerides to which EPA is bonded from these oils (Japanese Patent Laid-Open-to-Public Nos. 59644/1984 and 67241/1984). According to this process, the glycerides having the EPA content of up to about 25% can be separated from the oils. There are also known separation and purification processes by chromatography, solvent extraction and molecular distillation. However, such processes result in the production of glycerides having the EPA content as low as about 30%.
Under the circumstances, it has been demanded in the art to obtain glycerides rich in EPA, since digestion and absorption of EPA are said &o be advantageously performable when EPA is present in glyceride form. However. There are not known glycerides having the EPA content of higher than 30%, particularly those to which only EFA has bonded.
The applicant has already disclosed in his own prior patent application (Japanese Patent Application No. 162849/1984) the glycerides having the EPA content of higher than 30% and processes for the preparation thereof. However, there is still left much room for study and development of such glycerides when used as fat and oil components of margarine in an effort to allow the margarine to solidify more easily.
As is already known, fish oils undergo autoxidation in the atmosphere to bring about a decrease in nutritive value and bad taste. Such is also the case with EPA containing fat and oil components obtained by concentration from fish oils and the like. This degradation phenomenon proceeds by free radical chain reaction, whereby hydroperoxide accumulates in fats and oils and decomposition products thereof form the cause of toxicity and unpleasant odor. On that account the use of fish oils of EPA containing fat and oil components is rather limited.
Now an interest has been evinced in the use as supplementary foods for nutrition of glycerides of EPA prepared by concentration from fish oils and also the use of said glycerides as food additives has been taken into consideration. However, no food products incorporated with the glycerides of EPA have been put to practical use.
As mentioned previously we have already proposed glycerides having a high bonding ratio of EPA and processes for preparing the same. In the glycerides of EFA prepared by these processes, however, acyl radical of lower fatty acids derived from the lower fatty acid triglycerides which are the starting material inevitably remains. Because of the presence of the acyl radical of lower fatty acids, the resulting glycerides of EFA are low in melting point. On that account, there was a problem when the resultant glycerides of EPA were used as raw materials for the preparation of solid type fat and oil product such as margarine, shortening, etc. Accordingly, there has been an increasing demand for glycerides of EPA which are higher in melting point, i.e., those which are readily subject to solidification.